Say beside a composition that it changes only the bus's user list (issue 1943; the review's A2, for issue 1906)

A revision that changes only the user list is written into the bus node's want at once, outside the record hold
(ADR 0539 clause 7), so the assigner must tell it apart from a move that recreates or moves data.

go/delivery/composed.go

@@ -141,14 +141,19 @@ func checkDigest(digest, of string) error {
 // own choice (`upgrade` with policy) included. Rewritten when the policy changes. Empty on a composition made by hand
 // (mesh-compose), whose want the operator writes.
 type ComposedDigest struct {
-	V          int       `json:"v"`
-	Digest     string    `json:"digest"`
-	Judgement  Judgement `json:"judgement"`
-	Against    string    `json:"against,omitempty"`
-	Words      string    `json:"words,omitempty"`
-	Policy     string    `json:"policy,omitempty"`
-	PolicyFrom string    `json:"policy-from,omitempty"`
-	PolicyWhy  string    `json:"policy-why,omitempty"`
+	V         int       `json:"v"`
+	Digest    string    `json:"digest"`
+	Judgement Judgement `json:"judgement"`
+	Against   string    `json:"against,omitempty"`
+	Words     string    `json:"words,omitempty"`
+	// UserListOnly says the composition differs from the one the node's have names only in the bus's user list (the
+	// bus module's file `<module>.bus-users`), whatever the judgement says of its mount: the assigner writes such a
+	// revision into the bus node's want at once, outside the record hold, at the fingerprint the node runs (ADR 0539
+	// clause 7).
+	UserListOnly bool   `json:"user-list-only,omitempty"`
+	Policy       string `json:"policy,omitempty"`
+	PolicyFrom   string `json:"policy-from,omitempty"`
+	PolicyWhy    string `json:"policy-why,omitempty"`
 }
 
 // The upgrade policies and their sources a composition's value names: catalogue.PolicyRoll, PolicyTogether and

go/delivery/composed_keys_test.go

@@ -82,6 +82,7 @@ func TestComposedDigestValue(t *testing.T) {
 		{Digest: digest, Judgement: JudgedCannot, Words: "the composition the node runs is gone"},
 		{Digest: digest, Judgement: JudgedNeither, Policy: "record", PolicyFrom: "person", PolicyWhy: "the operator: its data"},
 		{Digest: digest, Judgement: JudgedNeither, Policy: "roll", PolicyFrom: "default"},
+		{Digest: digest, Judgement: JudgedNeither, Against: against, UserListOnly: true, Words: "only the bus's user list changes"},
 	} {
 		raw, err := EncodeComposedDigest(v)
 		if err != nil {